Mercury cathode discharge tube



March 28, 1939. LEMS 2,151,979

MERCURY CATHODE DISCHARGE TUBE Filed Dec. 16, 1936 INVENTOR. HENDRIXLEMS ATTORNEY.

Patented Mar. 28, 1939 PATENT OFFICE 2,151,979 MERCURY CATHODE DISCHARGETUBE Hendrik Lems,

hoven, Netherlands Eindhoven, to N. V. Philips Gloeilampenfabrieken,

Netherlands, assignor Eind- Application December 16, 1936, Serial No.116,198 In Germany December 16, 1935 7 Claims.

My invention relates to mercury cathode discharge tubes, and moreparticularly to a resilient member for use in such tubes.

Mercury cathode discharge tubes such as the rectifiers described in thecopending U. S. Patent application Ser. No. 67,155 to J. G. W. Mulder,filed March 4, 1936, comprise a movable member, for instance an ignitionelectrode, which is mechanically connected to a stationary body by aresilient member which also serves as an electrical connection betweenthe movable member and a supply lead.

Such a resilient member must have the desired resiliency and also a lowresistivity to allow for the passage of current, and it has beenproposed to make same of heat-resistant material, such as molybdenum.However, when members of such material are given the small cross sectionnecessary to obtain the required resiliency, they will have such a highelectrical resistance that they may be permanently deformed by the heatproduced by the passage of the currents normally used in such devices.

The main object of my invention is to provide a resilient member havingthe required resiliency while at the same time having a low resistivity.

A further object of my invention is to provide, a resilient member whichwill not be affected by the mercury vapor. I

In accordance with my invention I use as the resilient member, a bodyhaving a core of a. ma-

terial whose resistivity is substantially lower than that of themolybdenum, and I protect this core against the influence of the mercuryby providing the same with a protective coating of a metal whichamalgamates not at all or only to a slight extent with mercury.

To reduce the impact at the end of the stroke of the movable member, Iprovide a second resilient member, which however may be of aheat-resistant spring material as it does not carry current.

In order that my invention may be clearly understood and readily carriedinto effect, I shall descibe same more fully with reference to theaccompanying drawing, in which:

Figure 1 is a sectionized view of a mercury vapor rectifier embodyingthe invention, and

Fig. 2 is a sectional view on an enlarged scale of a portion of Figure1.

The rectifier shown in Figure 1 comprises an envelope having acup-shaped metal portion l containing a mercury cathode 3, and a glassportion 2 hermetically sealed to the metal portion at [5 and forming atubular protuberance 50.

Hermetically sealed in the top of portion 2 are two metal discs 5 and B,for instance of chrome iron. Supported from disc 5 is a main anode Isurrounded by a cylindrical screen l6 oi molybdenum which serves toprotect the seal l5 from 5 the discharge.

The rectifier is artificially cooled and for this purpose a jacket llsurrounds the metal portion l and is provided with an inlet passagewayl8 and an outlet passageway IQ for the passage of 10 a suitable coolingmedium such as water. A stud 20 passes through the bottom of the coolingjacket H in a liquid-tight manner and serives to secure same to themetal portion l and also as a supply lead for the mercury cathode 3.

Supported by screen It is a guide tube 9 in which is slidably disposed arod 8 of conductive material carrying on its lower end an ignitionelectrode 4. The upper portion of rod 8 is guided in the upperprotuberance of glass portion 2 and 20 carries a. cylindrical plungerll] of magnetic material, such as soft iron, which plunger ismechanically and electrically connected to a stationary core I2 by ahelical spring ll. Surrounding the spring H and secured to the core I2is a 25 second helical spring M.

The core i2 is secured to the lower end of a conductive member 25 whoseupper end is secured to disc 6 and connected therethrough to terminal26. For moving the anode 4 in a vertical direction a coil l3 surroundsthe protuberance 50. The coil l3 has a lead 21 connected to terminal 26,and a lead 30 to be connected to a supply of ignition voltage (notshown).

As shown more clearly in Fig. 2, the helical spring I l comprises a core28 of a material whose resistivity is less than that of molybdenum; forinstance copper, silver or an alloy consisting substantially of one ofthese metals. Such materials which have a resistivity less than 0.04 ohmper meter for a cross section of 1 square millimeter, have acomparatively low resiliency and are capable of withstanding only asmall amount of heat. However, their resistivity is so low that the heatproduced by the passage therethrough of currents of the normal value, isso small as not to afiect the resiliency. On the other hand, the springI l is so arranged in the tube that its resiliency will not bedeleteriously afiected by the heat produced in other ways, such as bythe heat of the arc.

As the metals of low resistivity such as used for the core 28 would beattacked if disposed within the envelope, the core 28 is provided with acoating 29 of a material which amalgamates not at all or only to a verysmall extent with mercury, for example chromium or nickel. Thus it isseen that by using a core of a material of low resistivity and byprotecting this core by a coating, the resiliency of the spring I I willnot be afiected during the operation of the rectifier.

The spring 14 serves to reduce the impact which might occur at the endof the stroke of the plunger l0, and as no current passes through thisspring it may be made of a much more resilient material than that usedfor the spring II, for instance a heat-proof spring material, such asmolybdenum.

While I have described my invention in connection with specific examplesand applications, I do not wish to be limited thereto but desire theappended claims to be construed as broadly as permissible in view of theprior art- What I claim is:

1. A discharge tube comprising an envelope, a mercury cathode and amovable member within said envelope, and means to move said movablemember comprising a resilient member within said envelope and serving asa current supply conductor to said movable member, said resilient membercomprising a resilient core of a metal having a resistivity less thanthat of molybdenum, and a thin coating of a metal substantiallyunaffected by mercury, said coating serving solely to protect the coreagainst the influence of the mercury.

2. A discharge tube comprising an envelope, a mercury cathode, a mainanode and a movable ignition electrode Within said envelope, and meansto move said ignition electrode comprising a resil ient member withinsaid envelope and serving as a current supply conductor to saidelectrode, said member comprising a resilient core of a metal having aresistivity less than that of molybdenum, and a thin coating of a metalsubstantially unaffected by mercury, said coating -serving solely toprotect the core against the influence of the mercury.

3. A discharge tube comprising an envelope, a mercury cathode and amovable member within said envelope, and means to move said membercomprising a resilient member within said envelope and serving as acurrent supply conductor for said movable member, said resilient membercomprising a resilient core of a metal having a resistivity less thanthat of molybdenum, and a thincoating of a metal substantiallyunaffected by mercury, said coating serving solely to protect the coreagainst the influence of the mercury, and a second resilient member ofheat-resistant spring metal acting upon said movable member only duringa portion of its movement.

4. A discharge tube comprising an envelope, a mercury cathode and amovable member within said envelope, and means to move said movablemember comprising a resilient member within said envelope and serving asa current supply conductor for said movable member, said resilientmember comprising a core of a metal having a resistivity less than thatof molybdenum, and a thin coating of nickel, said coating serving solelyto protect the core against the influence of the mercury.

5. A discharge tube comprising an envelope, a mercury cathode and amovable member within said envelope, and means to move said movablemember comprising a resilient member within said envelope and serving asa current supply conductor for said movable member, said resilientmember comprising a core of a metal having a resistivity less than thatof molybdenum, and a thin coating of chromium, said coating servingsolely to protect the core against the influence of the mercury.

6. A discharge tube comprising an envelope, a mercury cathode and amovable member within said envelope, and means to move said movablemember comprising a resilient member within said envelope and serving asa current supply conductor to said movable member, saidresilient membercomprising a core of a metallic substance whose resistivity is less thanthat of a molybdenum, said substance having silver as its majorconstituent, and a thin coating of a metal substantially unaffected bymercury, said coating serving solely to protect the core against theinfluence of the mercury.

7. A discharge tube comprising an envelope, a mercury cathode and amovable member within said envelope, and means to move said movablemember comprising a resilient member within said envelope and serving asa current supply conductor for said movable member, said resilientmember comprising a core of a'metallic substance having a resistivityless than that of molybdenum, said substance having copper as its majorconstituent, and a thin coating of a metal sub stantially unafiected bymercury, said coating serving solely to protect the core against theinfluence of the mercury.

HENDRIK LEMS.

